1. Field of the Invention
The present invention relates to a brush abrasion detector of a vehicle generator to be mounted on a vehicle such as automobile, auto-truck, electric train or the like.
2. Description of the Related Art
FIG. 11 is a diagram showing arrangement of a conventional brush abrasion detection circuit that detects a limit of abrasion of a brush in a vehicle AC generator, and raises the alarm for the detected limit and displays it, which is an art disclosed, for example, in the Japanese Patent Publication (unexamined) No. 101549/1982.
Operation of the conventional brush abrasion detection circuit, shown in FIG. 11, is described.
When a key switch 105 is closed, an excitation current flows from a battery 104 through the key switch 105, a brush (+) 109, a field winding (also referred to as a rotator winding) 102, a brush (−) 110 and a power generation control device 108. This current brings the field winding 102 in DC excitation (first control mode).
In such a state, when the rotator winding 102 is rotated and driven due to rotation of an engine not shown, voltage is induced to an armature winding (also referred to as a rotator winding) of three-phase star connection. Power generation output therefrom charges the battery 104 via a three-phase full-wave rectifier 103, while an excitation current flows from an auxiliary rectifier 107 to the field winding 102.
As a result, current flowing through a PL (pilot lamp) 106 is caused to reduce, and the PL (pilot lam) 106 having been in the state of lighting is turned off, whereby a vehicle driver can know the fact that a generator is in the state of power generation.
When rotational speed of the field winding 102 increases further, the power generation control device 108 is switched to a second control mode to control an excitation current flowing through the field winding 102 in order to make voltage of the battery 104 constant.
At this time, when either of the brush (+) 109 or brush (−) 110, which supplies current to the field winding 102, approaches the limit of abrasion, and the supply of excitation current is stopped, the power generation is stopped as well.
The foregoing conventional brush abrasion detector is provided with a photoelectric detector, e.g., a projector 113 and a photo-receiver 114 acting as a brush abrasion limit detecting part in the proximity of the brush (+) 109 and the brush (−) 110.
When the brush (+) 109 or the brush (−) 110 moves to a predetermined position due to abrasion, the photo-receiver 114 receives light from the projector 113, and carries out photoelectric transfer, thereby detecting a limit of abrasion of the brush.
FIG. 12 is a view showing a state in which the brush acting as a power feed member for use in the conventional abrasion detection circuit is held. For example, the brush (+) 109 is pressed onto a part that is fed with an electric power, not shown, by e.g., a coil spring 126. This brush (+) 109 is arranged to move as a whole due to abrasion of the brush (+) 109 itself while keeping the power feed.
The projector 113 (such as LED) and the photo-receiver 114 (such as photo transistor) are located in opposition to each other via a space in which the brush (+) 109 is held as shown in FIG. 12. The brush (−) 110 is located in a like manner.
In addition, the brush holder 125 being provided with the projector 113, the photo-receiver 114 and the coil spring 126, holds the brush 109 movably in the state of being press-fitted to an internal space thereof.
As a result, normally the brush is interposed between the projector 113 and the photo-receiver 114, and the photo-receiver 114 receives no light. However, as the brush approaches the limit of abrasion, the photo-receiver 114 comes to receive the light from the projector 113 increasingly. Additionally, FIG. 12 shows the state of receiving the light.
Current flows through the photo-receiver 114 responsive to the fact that the photo-receiver 114 receives the light, and then a transistor 115 amplifies this current and a Zener diode 118 brings it into a constant voltage.
Then, this constant voltage serves as an operation power supply for an astable multi-vibrator 112.
On the other hand, as an input to the foregoing astable multi-vibrator 112, the current having made the transistor 116 in ON state from a neutral point 111 via a diode 119 and a resistor 124, flows to the astable multi-vibrator 112 via a resistor 123.
The transistor 116 comes to be in the state of on (ON) or off (OFF) in accordance with a low level or a high level of the astable multi-vibrator 112, and further a transistor 117 comes to be in ON/OFF state. The PL (pilot lamp) 106 lights only when the transistor 117 is in ON state.
Accordingly, when the brush (+) 109 or the brush (−) 110 approaches the limit of abrasion, the astable multi-vibrator 112 oscillates at a low frequency, whereby the PL (pilot lamp) 106 comes to be in the state of a periodic flickering, that is, in the state of detecting and displaying the limit of abrasion.
In addition, as another conventional method for detecting the limit of abrasion of brush, the following brush abrasion detector is proposed in the Japanese Laid-open Utility Model Publication No. 44404/1982. In this detector, a brush, in which a detection electrode is implanted up to a position where the abrasion of brush is allowable, is attached so that a lower end face of the brush may be in contact with a commutator of an electric rotating machine, and alarm means is connected between the detection electrode and a power supply for the electric rotating machine. In response to the fact that the detection electrode is brought in contact with the commutator due to abrasion of brush, a predetermined voltage is applied to the alarm means to give an alarm.
However, in the conventional device (brush abrasion detection circuit) proposed in the Japanese Patent Publication (unexamined) No. 101549/1982, a detector consisting of a projector (light emitting diode), a photo-receiver (photo transistor) and the like is required in order to detect the abrasion of brush. Moreover, to dispose these detectors at a brush holder, it is necessary to apply machining to the brush holder.
In the conventional brush abrasion detector proposed in the Japanese Laid-open Utility Model Publication No. 44404/1982, although no detector consisting a projector and a photo receiver is required, it is necessary to implant directly in the brush a detection electrode for detecting the limit of abrasion thereof. Therefore, application of complicated machining is necessary as well.
Moreover, in the above-described conventional device, normally scrap or dust of abrading brush are produced and accumulated accompanied by the abrasion of brush.
Consequently, the accumulated scrap or dust becomes a factor of reducing operation reliability of a detector or detecting element disposed in the proximity of the brush at the time of the limit of abrasion of brush.